342 COX, REIBLING, AND REYES. 
from mixture 19. The cracks were caused by shrinkage due to 
the tendency of volcanic tuff to flux and melt at the maximum 
temperature used. In spite of its cracked condition, this brick 
withstood a pressure of 3,400 pounds per square inch (240 kilo- 
grams per square centimeter). 
A high content of soluble silica, such as is characteristic of 
these volcanic tuffs, favors the development of great strength. 
On the other hand, most of the individual grains are soft, and 
soft grains are detrimental to the strength. For best results 
the volcanic tuff should be mixed with hard-grained sands or 
crushed rock, and for this purpose it is especially adapted both 
on account of the high content of soluble silica and the ease with 
which it can be obtained, pulverized, and molded for a maximum 
strength. 
TABLE XIII.—Sand-lime brick made with a mixture of 1 part of pulverized 
Guadalupe stone and 3 of natural Pasig sand. 
Degree of fineness in per cent through the Compressive 
specified sieves. ton Molding strength. 
Mixture aa ies pea 
No. reat square Per 
No. 20. | No. 40. | No. 80. | No. 100. | No. 200. 2 inch. Total. square 
inch. 
Hours. | Pounds. | Pounds. | Pounds. 
22 99.0 79.0 32.5 26.0 16.5 8.0 7, 640 13, 200 3,300 
22 99.0 79.0 32.5 26.0 16.5 8.0 10, 000 13, 600 3, 400 
The advisability of using voleanic tuff or beach sand in con- 
junction with other available siliceous materials rather than alone 
is further substantiated by the fact that the sand-lime bricks 
made from either alone possess the least density and absorb the 
most water. 
Quarry débris is also available. The amount of rock and 
crushed stone used in Manila for breakwaters, macadam roads, 
and concrete is considerable, and at present 4 quarry sites are 
operated to meet the demand; namely, (1) the Rizal, (2) the 
Manila city quarries at Talim Island, (8) Carabao Island quarry 
in the south channel entrance of Manila Bay, and (4) the Sisi- 
man quarry near Mariveles. 
Crusher-run Sisiman stone contains a large amount of rock 
flour and sand which is not suitable for road surfacing on account 
of its poor cementive value. At present this quarry débris is 
a waste product. Sisiman rock is a gray andesite, while the 
stone in the other quarries is basalt. Neither contains free silica, 
but both are high in soluble silica. Owing to this high content 
